Some antibiotics having .beta.-lactamase inhibitory activity or .beta.-lactamase inhibitory agents have so far been known. For example, the following have been reported: MC696-SY2-A and B isolated from the culture broth of the MC696-SY2 producing strain belonging to the genus Streptomyces (U.S. Pat. No. 3,928,569: Derwent CPI 15846V), MM4550 or MM13902 isolated from the cultured materials of the MM4550 or MM13902 producing strain which belongs to the genus Streptomyces (German Appln. DOS No. 2,513,855: Derwent CPI 67221W; German Appln. DOS No. 2,513,854: Derwent CPI 67720W), clavulanic acid isolated from the cultured materials of Streptomyces clavuligerus (German Appln. DOS No. 2,517,316: Derwent CPI 72840W), and the like. The antibiotic thienamycin having a penicillin-like chemical skeleton and the derivatives thereof have also been reported (U.S. Pat. No. 3,950,357: Derwent CPI 31696X; German Appln. DOS No. 2,652,677: Derwent CPI 40282Y; Belgian Pat. No. 848,346: Derwent CPI 34505Y; Belgian Pat. No. 848,349: Derwent CPI 34507: German Appln. DOS No. 2,652,680: Derwent CPI 40283Y; German Appln. DOS No. 2,652,675: Derwent CPI 40280Y: German Application DOS No. 2,652,674: Derwent CPI 40279Y; German Appln. DOS No. 2,652,676: Derwent CPI 40281Y).